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This post is in continuation in my last post. In my last post, I discussed various ways to create custom object in JavaScript. I’ll advise you to go through that if you didn’t get a chance to have a look then you can go through it. Please find the link below

In this post, We will discuss, how we can use other features of Object Oriented concepts in JavaScript. Today I’ll discuss one of the main concepts of Object Orient Programming that is Inheritance.

So how can we use Inheritance with JavaScript ?

Various ways and plugins are available that provides similar ways to use Inheritance that we have used in other object oriented language. But the prototype based Inheritance is used most.

JavaScript is a object based language that is based upon Prototype based programming. It is free from Class and completely rely on objects only .

Did you hear earlier that What is Prototype based language or what is Prototype based programming?

I would say this is just another way to provide object oriented feature by a language. As per wiki

“Prototype-based programming is a style of object-oriented programming in which classes are not present, and behavior reuse (known as inheritance in class-based languages) is performed via a process of cloning existing objects that serve as prototypes. This model can also be known as classless, prototype-oriented or instance-based programming. Delegation is the language feature that supports prototype-based programming”.

So let’s start learning. To create a Class in JavaScript, we are required to create a function that we also used to call a Constructor. I’ll use the word constructor in my further discussion. So Let’s create a Constructor called person

Line 5- What it will display ? It displays I am an employee because ToString is available at both current and parent. But because the objEmployee holds the instance of derived class so the overridden method is called.

Line 6- Here DisplayResidence is not defined in Employee so it calls the base class(Person) method and displayed.

Line 7- DisplayRole is added in Employee object only and it shows ‘My role is development and implementation‘.

Line 8 – To check more on the type I added the last two lines. As objPerson is instance of Person only so it shows true.

Line 9 – As Employee inherits Person so it also shows true but if you delete the below line ….

<br />Employee.prototype = new Person();<br />

then it’ll show false as it does not inherit person any more.

Now you must have got enough Idea about prototype based inheritance in JavaScript.

There is one more way to add a method to and existing constructor as Person has two methods and that we defined as nested class. You can write that in the following way as well

Whenever we create an instance using the new Operator, It creates all the properties/methods and also has internally a variable called __proto__ (double underscore at both side) this is the variable which is responsible for the inheritance feature. So let’s say I created a instance of Employee as

var objEmployee = new Employee();

It’ll be having two methods/properties as defined and on __proto__ as

ToString

DisplayRole

__proto__

Just because I have written also as

Employee.prototype = new Person();

The __proto__ variable gets assigned to the person instance. This __proto__ used to determine the prototype chain and return the property values. This allows us to access the base class methods and public properties.

As I talked about prototype chain, means as soon as I assign

Employee.prototype = new Person();

a proto variable gets available to us that can be be further used for inheritance. So lets create another constructor as

Most of the web developer’s answer would just less than infinite. This is the most used keyword and become rescue tool when we stay late at office to resolve a silly JavaScript issue. Alert prompts user a popup with some information. Earlier it was also used heavily for showing validation error messages.

But do you know what all are other popup options available with JavaScript?

These are in total three as below

Let’s discuss one by one

Alert

It is the simplest one and most widely used to show some message to user in one way. Once the message on browser, it shows OK button which is required to be pressed before moving further as

Syntax

Syntax is pretty simple

alert("Your meesage to user");

Confirm

This is another important message box which instead of just showing a message to user, it also accepts the user’s response. It is used to take a Boolean response (true/false) from the user. When displays it show two buttons Ok and Cancel. Ok return true and Cancel returns false. Lets see it

Syntax

Prompt

This is another popup message box which is used least. But this can be very helpful in certain scenarios. This allows to take some input from the user. When it is shown to user, it provides an input box in popup where user can enter some text with OK and Cancel button. If OK is pressed then the entered value is passed to the backend else it returns null. It also allows us provide a default value in text box.

I have used Internet Explorer for this example and if you have used alert or any of them with earlier version of IE like IE 6/7, its looks much better now. It looks different on different browser because its the browser which shows its own popup. Although in most of the cases, we don’t use these popup due to its limitation and look n feel but can help in many scenarios and suitable for small applications.

Many developers still put their data at client side in multiple variables and some times it becomes very tough to manage them. If we store the data in object format then it becomes very easy to manage and control it. We can have similar model as we use at server side, it provides consistency of the data model in our application.

So today we’ll see various ways to store the data in Object format at Client side.

A Simple way:

We can create a normal object and can encapsulate related data in a single object. To create a simple object, you just need to assign a variable with new Object() and create the properties according to our requirement and assign the values as

Here as you can see it is an object which contains the details of an person but here we didn’t define any class (as we do in C#) then we create an object assign some values in that. But we just created a object and created properties on the fly. Now obviously, while reading the object, you might not get any intellisense on some editor and we need to remember the name of the properties. And if we wrongly typed the property name then we’ll get an error at run time.

Because JavaScript is loosely coupled language. There is no way if we create similar object and check whether they are similar type of object. Also it is impossible to identify the object that you are using is actually of what type.

But there are more standard ways to Create a Type. We’ll discuss in coming section. First, we are going to discuss

Closure
Closure is function that encapsulate a class. Actually closure is not a normal function but it contains other functions and you can say it is a nested function. Inner functions actually constitutes its properties and methods. It provides an elegant way to create multiple instances of a type like person. It provides exactly similar behavior like class and object. Let’s create a closure

Now let’s use the person and person instantiate it. As you can see that it is taking three parameters, fisrtName, lastName and age. So you need pass the values while instantiating it. Using it, you can create an instance similar like C# as

So you can see, How I created instance. I have created a setter and getter to set and get the properties.

Lets’s discuss another way.

Prototype:

Prototypes provides another way to create custom objects in JavaScript. Every JavaScript object has public prototype property . This actually exposes the public interface of the object. Using this feature, we can add some public properties and methods to a JavaScript object. Let’s see it with example

In C#, creating random number is simple and provides multiple options. Random class is used for the same, it’s Next method used to create random number. It also takes min and max value as parameter to create a random number in a range.

In Javascript it is more simple :). Let’s see that

Math.random is used to create a random number. But it returns a decimal numal number between between 0 (including) to 1(excluding). Let’s see that

function displayRandom()
{
alert(Math.random());
}

It will create different number each time. So if you want to create a random number say upto 10000 then you can get it by simply writing

var randomnumber = Math.random() * 10000;

Pretty simple Right!!

But it will always create a number less than 10000 (till 9999.999..) and if you take the integer part then the max value you will get 9999. But what if want inclusive of 10000?

Then you can leverage the other method Math.ceil which generates the ceiling number as

Math.ceil(6.0001)

Math.ceil(6.203)

Math.ceil(6.0001)

Math.ceil(6.9001)

For all you will get 7. So if you write the original method as

function displayRandom()
{
alert(Math.ceil(Math.random()));
}

You will get the number between 0 to 10000 both inclusive. You can also use Math.floor or Math.abs to have your own logic for getting random number in a range.

This is small post but I found it bit interesting and useful sometime.

Dependency Injection (DI) is one of the hottest terms being used in software development nowadays. Most of the application developers talking about this and try using it in their applications. One of the key reasons Agile methodology, as it is used in almost every project in one or other way and DI easily fits into this model and help in achieving its goal. I have been getting many request to write about DI in AngularJS so let’s start exploring that.

Note – This post is a part of series of posts on AngularJS and it is 16th one. Click here to view all the post. Apart from that you can also use the navigation links for next and previous post in each post at the bottom to check all.Continue reading →

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C# Corner Delhi chapter is hosting next event on 23rd November at Noida and Become Better JS developer in a day. This time we are discussing various hot Client side libraries jQuery, Node.js and Knockout.js. After all the session, there will be Test which results will be online. This will be a full day event with full hands on exercises etc.